#include <cstdio>
#include <cstring>

using namespace std;

const int maxn = 100010;

int main() {
	int choice[maxn] = {0}, a[maxn];
	int n, target = -1;
	scanf("%d", &n);
	for (int i = 0; i < n; i++) {
		scanf("%d", &a[i]);
		choice[a[i]]++;
	}
	for (int i = 0; i < n; i++) {
		if (choice[a[i]] == 1) {
			target = a[i];
			break;
		}
	}

	if (target == -1) {
		printf("None\n");
	} else {
		printf("%d\n", target);
	}

	return 0;
}
